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In Reply to: RE: There is one other thing helping this Eico HF-87 sound so good posted by airtime on September 13, 2016 at 18:48:39
"The only thing I have to the Hf-50 so far is put in a 51uf solen poly off the GZ34. I also put in some Vitamin Q couplers and and a decoupler..Everything else is original including the downstream can.It's a nice sounding amp but the HF-87 murders it right now for dynamics and that's running JJ KT77s..They sound really nice if you can get a good safe pair..I prefer the Genelex RI KT77s but still it's a nice sounding tube.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Follow Ups:
"The only thing I have to the Hf-50 so far is put in a 51uf solen poly off the GZ34. I also put in some Vitamin Q couplers and and a decoupler..Everything else is original including the downstream can"
Which of the two chokes would you advise for a HF-50?
Any other "low hanging fruit" for the HF-50? Including the "downstream can"?
FWIW… I'm running El 37's currently (with a variac).
" This is kind of tricky because you will notice that the output tubes source go directly to the GZ34.I plan on doing the Dave Gillepsie mod to all four of my Hf50s and my one pair of HF60s.If you add a choke series with the rectifier up to the output trafo B+,I would use the .5hy at 300ma as that will fit under the chassis..Wheezer things we should use a 30hy to 40 hy for the earlier stages so I'm looking into that as well.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I made the assumption that you are modding all your HF-50's to 6550's?
Any comment on using KT77's and following the front end and power supply of Dave's mod?
A couple of questions:
Are you increasing the 20mfd caps on the B+ due to the .5Hy choke?
Is the DC resistance of the .5Hy choke the same as the 3Hy on DG's mod, as this would impact the values of the R24.
Lokie
Iam modding it to 6550s.. I use a 51uf film cap,a big solen can and I will be using a choke as well..Keep in mind the that the originals were a pair of 20uf lytics in parallel for the first..The output trafo goes directly into the rectifier and the 51uf Solen.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I bet it sounds especially nice missing a 6CA7
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I bet it sounds especially nice missing a 6CA7
I took both KT77s out of the HF87 as well as the 6SN7 because I was comparing one channel of the McShaned HF87 to the HF50.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I sure like that tube lineup.
EF86 6SN7 EL34
After all these years, it still doesn't get much better than that!
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Buy Chinese. Bury freedom.
I changed over to the Gen RI KT77 from the metal based EL34 and the KT77s are just plain better all the way thru.The EL34s sound fine if you listen and let your hearing mechanism tube and acclimate to them but the minute go to the KT77s,you gain top and bottom dynamics and definition that can't be denied..Even the JJ KT77s are fabulous,just not quite as good as the Genelex sonically.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
There could be many reasons for that other than the 77s simply being better. Have you attempted to measure the performance difference between the two types? Was NFB readjusted to accommodate differences?
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Buy Chinese. Bury freedom.
"There could be many reasons for that other than the 77s simply being better. Have you attempted to measure the performance difference between the two types? Was NFB readjusted to accommodate differences?"
That is very true and I seem to remember doing a sweep test with the EL34s where the distortion product broadened out in the higher frequency ranges.
There is a reason that this happened and part of that could be the fact that EL34s might not like being run in UL as they would in pure pentode.
I have also come to the conclusion that Peter Walker of Quad chose the KT66 kinkless Tetrode as opposed to the EL34 to power his new speakers for the reasons I had mentioned.He could have easily chosen the less expensive and easier to drive EL34 if he thought it would produce the detailed and open sound he wanted out of his ESL-57 speakers at the time.
Keep in mind that the EL34 was out at the same time that the KT66 was.
I'm going to once again measure the EL34s on the sweep analyzers and see what happens.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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